1. Field of the Invention
The invention relates in general to a driving circuit, and more particularly to a display driving circuit.
2. Description of the Related Art
Referring to FIG. 1, a partial diagram of a conventional display driving circuit is shown. The conventional display driving circuit 10 comprises a positive gray scale display reference voltage generating circuit for gamma correction of red color channels 12a, a positive gray scale display reference voltage generating circuit for gamma correction of green color channels 12b, a positive gray scale display reference voltage generating circuit for gamma correction of blue color channels 12c, a negative gray scale display reference voltage generating circuit for gamma correction of red color channels 12d, a negative gray scale display reference voltage generating circuit for gamma correction of green color channels 12e, a negative gray scale display reference voltage generating circuit for gamma correction of blue color channels 12f, a digital to analog converter (DAC) 13, a register for storing the information of gamma corrections 15, a data latch 16, a level shifter 17 and a buffer operational amplifier 18.
The positive gray scale display reference voltage generating circuits 12a, 12b and 12c respectively generate 256 positive gray scale display reference voltages for gamma correction of red color channels, 256 positive gray scale display reference voltages for gamma correction of green color channels and 256 positive gray scale display reference voltages for gamma correction of blue color channels according to the settings for the positive display reference voltages stored in the register 15. The negative gray scale display reference voltage generating circuits 12d, 12e and 12f respectively generate 256 negative gray scale display reference voltages for gamma correction of red color channels, 256 negative gray scale display reference voltages for gamma correction of green color channels and 256 negative gray scale display reference voltages for gamma correction of blue color channels according to the settings for the negative display reference voltages stored in the register 15.
The video signals of pixel data, R[7:0]/G[7:0]/B[7:0], are serially sent into the data latch. The data latch temporarily stores the pixel data of display line for each display channel. The outputs of the data latch are connected to the level shifter. The level shifter translates the power domain for the video signal. The DAC 13 outputs one of the display reference voltages to the buffer operational amplifier from the 256 display reference voltages generated by the gray scale reference voltage generating circuit according to it's input video signal. Finally, the multiplexer mux controlled by a polarity outputs a driving voltage VO outputted from the buffer operational amplifier 18 to provide large driving ability to drive display device.
In order to independently adjust the gamma correction for each of the color channels (red, green, blue), the conventional display driving circuit 10 needs at least 3 sets of gray scale display reference voltage generating circuits, wherein each set of gray scale display reference voltage generating circuit comprises a positive gray scale display reference voltage generating circuit and a negative gray scale display reference voltage generating circuit. However, such design occupies large chip area and consumes a lot of power consumption. Furthermore, the conventional display driving circuit 10 needs considerable metal routing traces for the gray scale display reference voltages in the layout of the circuit.